Spray two large loaf pans or six mini loaf pans with nonstick baking spray, then line the bottoms with parchment paper.
In a large mixing bowl, combine the flour, sugar, instant lemon pudding mix, baking soda, baking powder, and salt. Stir well so the leaveners and pudding mix are evenly distributed.
In a separate small mixing bowl, whisk together the eggs, milk, vegetable oil, and lemon juice until smooth.
Pour the wet mixture into the dry ingredients and stir gently until the flour is mostly moistened. Do not overmix.
Add the shredded zucchini, poppy seeds, and lemon zest. Fold just until combined.
Divide the batter evenly among the prepared pans.
Bake at 325°F for 50-55 minutes for two 9x5-inch loaf pans, or 30-35 minutes for six 5x3-inch mini loaf pans. The tops should feel set and a tester inserted near the center should come out with a few moist crumbs, not wet batter.
Cool the loaves in the pans for 10 minutes, then remove them to wire racks and cool before slicing.